Single Point Diamond Turning of Calcium Fluoride Optics

Abstract:

This paper aims to develop a cost-effective diamond turning process to obtain nanosmooth CaF₂ optics. Diamond tool wear was also carried out through a number of cutting trials. Three CaF₂ specimens (diameter of 50 mm and thickness of 5 mm, crystal orientation of (111)) were diamond turned on an ultra precision lathe (Moore Nanotech 350UPL) by a number of facing cuts. In the cutting trials feed rate varied from 1 μm/rev to 10 μm/rev. White spirit mist was used as the coolant. Cutting forces were measured by a dynamometer (Kistler BA9256). Surface roughness of the CaF₂ optics and tool flank wear were measured by a white light interferometer (Zygo Newview 5000) and a scanning electron microscope (FEI Quanta 3D FEG), respectively. It was found that using a feed rate of 1 μm/rev surface roughness Ra of 2 nm could be obtained. When the ratio of the normal cutting force to the tangential cutting force was lower than 1 tool wear would initiate. In diamond turning of calcium fluoride abrasive wear was the main tool wear mechanism. Using white spirit mist as thecoolant could avoid generation of thermal type brittle fracture on the machined CaF₂ surfaces.

• Periodical: Key Engineering Materials (Volume 516)
• Pages: 408-413
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.516.408
• Online since: June 2012
• Authors: Xi Chun Luo, Ji Ning Sun, Wen Long Chang, James M. Ritchie
• Keywords: Brittle Fracture, CaF₂ Optics, Diamond Tool Wear, Diamond Turning

References

[1] D.J. Ewing, Excimer lasers at 30 years, Opt. Photonics News 14 (2003) 26-31.

[2] D.L. Decker, D.J. Grandjean, J.M. Bennett, Optical and surface physical characteristics of diamond-machined infrared windows, NBS Spec. 562 (1979) 293–304.

[3] J. Yan, K. Syoji, J. Tamaki, Crystallographic effect in micro/nanomachining of single-crystal calcium fluoride, J. Vac. Sci. Technol. B22 (2004) 46-51.

DOI: 10.1116/1.1633770

[4] E.R. Marsh, B.P. John, J.A. Couey, J. Wang, R.D. Grejda, R.R. Vallance, Predicting surface figure in diamond turned calcium fluoride using in-process force measurement, J. Vac. Sci. Technol. B23 (2005) 84-89.

DOI: 10.1116/1.1839897

[5] Y. Nambaa, N. Ohnishia, S. Yoshidaa, K. Harada, Y. Yoshida, T. Matsuo, Ultra-precision float polishing of calcium fluoride single crystals for deep ultra violet applications, CIRP Ann. -Manufacturing Technology 53 (2004) 459-462.

DOI: 10.1016/s0007-8506(07)60739-2

[6] J. Yan, J. Tamaki, K. Syoji, T. Kuriyagawa, Single point diamond turning of CaF2 for nanometric surface, Int. J. Adv Manuf Tech. 24 (2004) 640-646.

DOI: 10.1007/s00170-003-1747-2

[7] P. Blake, R.O. Scattergood, Ductile-regime machining of germanium and silicon, J, Am. Ceram. Soc. 73 (1990) 949-957.

DOI: 10.1111/j.1151-2916.1990.tb05142.x